>This task amounts to replacing the engine of a running car.

I hate this phraseology, and IMO it's a telltale sign of a new or inexperienced professional developer (another variation: "replace jet engine while in flight"). All non-greenfield development forbids breaking the existing system in order to make changes. This is a daunting responsibility, but it's inherent and assumed, so only college kids who have never had to maintain a running system before talk about it like it's noteworthy.

If someone needs a microservice architecture to support team growth, it just means they don't know how to manage a team, and have to let every dev or pair of devs have their own little kingdom.